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Introduction The design of off-line constant voltage, constant current (CVCC) power supplies using the NCP1014 for devices such as cell phones, hand tools, and similar battery chargers can present various challenges when low cost and circuit simplicity are required alongside good performance and high efficiency. A common issue involves deriving a straightforward yet effective Vcc source for the secondary control circuitry without increasing circuit complexity, adding extra secondary windings to the high-frequency switching transformer, or utilizing high-value current sense resistors. Most chargers within this category typically necessitate an output voltage ranging from 3 to 15 volts and are implemented using simple, low-cost flyback switch-mode topologies. A typical application is illustrated in Figure 1, which depicts a standard CVCC charger implementation detailed in ON Semiconductor's Reference Design TND329/D (5 W CCCV AC-DC Adapter GreenPoint Reference Design).

The NCP1014 is a versatile integrated circuit designed for off-line power supply applications, particularly suitable for constant voltage and constant current (CVCC) configurations. This device efficiently manages the power conversion process, ensuring that the output voltage remains stable while also providing current regulation as needed, which is essential for charging batteries safely and effectively.

In a typical CVCC charger design, the NCP1014 operates within a flyback topology, which allows for isolation between input and output, a critical feature for safety in consumer electronics. The flyback converter uses a transformer to store energy when the switch is closed and releases it to the output when the switch is open. This method not only simplifies the circuit but also minimizes component count, contributing to lower production costs.

The design aims to achieve an output voltage within the range of 3 to 15 volts, accommodating various battery types and charging requirements. The efficiency of the power supply is enhanced by optimizing the transformer design and selecting appropriate component values, including the current sense resistor, which plays a vital role in current regulation without introducing excessive losses.

To derive the Vcc for the secondary control circuitry, the design employs a simple approach that avoids additional complexity. Instead of using multiple secondary windings or high-value current sense resistors, the circuit can utilize a bootstrap configuration or a dedicated auxiliary winding, ensuring that the control circuitry receives the necessary voltage without compromising the overall design simplicity.

This design methodology aligns with the requirements for modern battery chargers, balancing performance, cost, and efficiency. The reference design provided by ON Semiconductor serves as a valuable resource for engineers looking to implement a reliable CVCC power supply solution, offering insights into component selection, layout considerations, and performance optimization techniques.Introduction The design of off-line constant voltage, constant current (CVCC) power supplies NCP1014 for cell phone, hand tool, and similar Battery Chargers CAN present several challenges if low cost and circuit simplicity are necessary, yet good performance and high efficiency are required. One typical problem is associated with deriving a simple yet effective Vcc source for the secondary control circuitry without resorting to additional circuit complexity, more secondary windings on the high frequency switching transformer, and using high value Current Sense resistors. Most chargers that fall in this category typically require an output voltage of 3 to 15 volts and are implemented with simple, low cost flyback switchmode topologies.

Typical Application Figure 1 shows a typical CVCC charger implementation which is described in detail in ON Semiconductor`s Reference Design TND329/D (5 W CCCV AC-DC Adapter GreenPoint Reference Design). 🔗 External reference